Surfaces, including microfluidic channels, with controlled wetting properties

ABSTRACT

The present invention generally relates to coating materials, including photoactive coating materials. In some aspects of the invention, a sol-gel is provided that can be formed as a coating on a microfluidic channel. One or more portions of the sol-gel can be reacted to alter its hydrophobicity, in some cases. For instance, in one set of embodiments, a portion of the sol-gel may be exposed to light, such as ultraviolet light, which can be used to induce a chemical reaction in the sol-gel that alters its hydrophobicity. In one set of embodiments, the sol-gel can include a photoinitiator, that upon exposure to light, produces radicals. Optionally, the photoinitiator may be conjugated to a silane or other material within the sol-gel. The radicals so produced may be used to cause a polymerization reaction to occur on the surface of the sol-gel, thus altering the hydrophobicity of the surface. In some cases, various portions may be reacted or left unreacted, e.g., by controlling exposure to light (for instance, using a mask). Such treated surfaces within a microfluidic channel may be useful in a wide variety of applications, for instance, in the creation of emulsions such as multiple emulsions.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/040,442, filed Mar. 28, 2008, entitled“Surfaces, Including Microfluidic Channels, With Controlled WettingProperties,” by Abate, et al., incorporated herein by reference.

GOVERNMENT FUNDING

Research leading to various aspects of the present invention weresponsored, at least in part, by the National Science Foundation. TheU.S. Government has certain rights in the invention.

FIELD OF INVENTION

The present invention generally relates to coating materials, includingphotoactive coating materials.

BACKGROUND

Glass-capillary microfluidic devices have recently enabled formation ofhighly monodisperse emulsions with a rich array of droplet morphologies,such as those disclosed in U.S. Provisional Patent Application Ser. No.60/920,574, filed Mar. 28, 2007, entitled “Multiple Emulsions andTechniques for Formation,” by Chu, et al., incorporated herein byreference. Such devices exhibit chemical robustness and precise control.

An emulsion is a fluidic state which exists when a first fluid isdispersed in a second fluid that is typically immiscible orsubstantially immiscible with the first fluid. Examples of commonemulsions are oil in water and water in oil emulsions. Multipleemulsions are emulsions that are formed with more than two fluids, ortwo or more fluids arranged in a more complex manner than a typicaltwo-fluid emulsion. For example, a multiple emulsion may beoil-in-water-in-oil (“o/w/o”), or water-in-oil-in-water (“w/o/w”).Multiple emulsions are of particular interest because of current andpotential applications in fields such as pharmaceutical delivery, paintsand coatings, food and beverage, chemical separations, and health andbeauty aids.

SUMMARY OF THE INVENTION

The present invention generally relates to coating materials, includingphotoactive coating materials. The subject matter of the presentinvention involves, in some cases, interrelated products, alternativesolutions to a particular problem, and/or a plurality of different usesof one or more systems and/or articles.

In one aspect, the invention is directed to an article. In one set ofembodiments, the article includes a sol-gel coating coated on at least aportion of a microfluidic channel. In another set of embodiments, thearticle includes a sol-gel coating coated on at least a portion of asubstrate.

The invention, in another aspect, is directed to a method. In one set ofembodiments, the method includes acts of exposing at least a portion ofa microfluidic channel to a sol, causing at least a portion of the solto gel within the microfluidic channel to form a sol-gel coating, andaltering the hydrophobicity of a first portion of the sol-gel coatingwithout altering the hydrophobicity of a second portion of the sol-gelcoating.

In yet another aspect, the invention is directed to a composition. Inone set of embodiments, the composition includes a photoinitiatorcoupled to a silane.

In another aspect, the present invention is directed to a method ofmaking one or more of the embodiments described herein, for example,photoactive coating materials such as those described herein. In anotheraspect, the present invention is directed to a method of using one ormore of the embodiments described herein, for example, photoactivecoating materials such as those described herein.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIGS. 1A-1F illustrate various coated microfluidic channels, accordingto various embodiments of the invention;

FIGS. 2A-2C illustrate FTIR and contact angle measurements of a coatedsubstrate, in another embodiment of the invention;

FIGS. 3A-3D illustrate AFM images of a coated microfluidic channel, inyet another embodiment of the invention; and

FIGS. 4A-4D illustrate the production of multiple emulsions, in oneembodiment of the invention.

DETAILED DESCRIPTION

The present invention generally relates to coating materials, includingphotoactive coating materials. In some aspects of the invention, asol-gel is provided that can be formed as a coating on a substrate suchas a microfluidic channel. One or more portions of the sol-gel can bereacted to alter its hydrophobicity, in some cases. For example, aportion of the sol-gel may be exposed to light, such as ultravioletlight, which can be used to induce a chemical reaction in the sol-gelthat alters its hydrophobicity. The sol-gel can include a photoinitiatorwhich, upon exposure to light, produces radicals. Optionally, thephotoinitiator may be conjugated to a silane or other material withinthe sol-gel. The radicals so produced may be used to cause acondensation or polymerization reaction to occur on the surface of thesol-gel, thus altering the hydrophobicity of the surface. In some cases,various portions may be reacted or left unreacted, e.g., by controllingexposure to light (for instance, using a mask). Such treated surfaceswithin a microfluidic channel may be useful in a wide variety ofapplications, for instance, in the creation of emulsions such asmultiple emulsions, for instance, as discussed in U.S. patentapplication Ser. No. 12/058,628, filed on Mar. 28, 2008, entitled“Emulsions and Techniques for Formation,” by Chu, et al.

The invention is described herein primarily in the context of coatingson microfluidic channels, coatings of particular hydrophobicity(lipophilicity) or hydrophobicity (lipophilicity), controllinghydrophobicity, coatings of particular thicknesses, etc. In some cases,fluorophilicity may be controlled, in addition to or instead ofhydrophobicity. It is to be understood that any of the various aspectsand options of the invention can be present, absent, and/or used aloneor in combination with any other aspects, option, example, orembodiment. For example, in one embodiment, more than layer of sol maybe applied to a surface, or a photoinitiator may be applied after thetreatment with another sol-gel mixture.

In one aspect of the invention, a sol-gel is coated onto at least aportion of a substrate. As is known to those of ordinary skill in theart, a sol-gel is a material that can be in a sol or a gel state. Insome cases, the solgel material may comprise a polymer. The sol statemay be converted into the gel state by chemical reaction. In some cases,the reaction may be facilitated by removing solvent from the sol, e.g.,via drying or heating techniques. Thus, in some cases, as discussedbelow, the sol may be pretreated before being used, for instance, bycausing some condensation to occur within the sol. Sol-gel chemistry is,in general, analogous to polymerization, but is a sequence of hydrolysisof the silanes yielding silanols and subsequent condensation of thesesilanols to form silica or siloxanes.

In some embodiments, the sol-gel coating may be chosen to have certainproperties, for example, having a certain hydrophobicity. The propertiesof the coating may be controlled by controlling the composition of thesol-gel (for example, by using certain materials or polymers within thesol-gel), and/or by modifying the coating, for instance, by exposing thecoating to a condensation or polymerization reaction to react a polymerto the sol-gel coating, as discussed below.

For example, the sol-gel coating may be made more hydrophobic byincorporating a hydrophobic polymer in the sol-gel. For instance, thesol-gel may contain one or more silanes, for example, a fluorosilane(i.e., a silane containing at least one fluorine atom) such asheptadecafluorosilane or heptadecafluorooctylsilane, or other silanessuch as methyltriethoxy silane (MTES) or a silane containing one or morelipid chains, such as octadecylsilane or other CH₃(CH₂)_(n)-silanes,where n can be any suitable integer. For instance, n may be greater than1, 5, or 10, and less than about 20, 25, or 30. The silanes may alsooptionally include other groups, such as alkoxide groups, for instance,octadecyltrimethoxysilane. Other examples of suitable silanes includealkoxysilanes such as ethoxysilane or methoxysilane, halosilanes such aschlorosilanes, or other silicon-containing compounds containinghydrolyzable moieties on the silicon atom, such as hydroxide moieties.In general, most silanes can be used in the sol-gel, with the particularsilane being chosen on the basis of desired properties such ashydrophobicity. Other silanes (e.g., having shorter or longer chainlengths) may also be chosen in other embodiments of the invention,depending on factors such as the relative hydrophobicity orhydrophilicity desired. In some cases, the silanes may contain othergroups, for example, groups such as amines, which would make the sol-gelmore hydrophilic. Non-limiting examples include diamine silane, triaminesilane, or N-[3-(trimethoxysilyl)propyl]ethylene diamine silane. Thesilanes may be reacted to form networks within the sol-gel, and thedegree of condensation may be controlled by controlling the reactionconditions, for example by controlling the temperature, amount of acidor base present, or the like. In some cases, more than one silane may bepresent in the sol-gel. For instance, the sol-gel may includefluorosilanes to cause the resulting sol-gel to exhibit greaterhydrophobicity, and other silanes (or other compounds) that facilitatethe production of polymers. In some cases, materials able to produceSiO₂ compounds to facilitate condensation or polymerization may bepresent, for example, TEOS (tetraethyl orthosilicate). In someembodiments, the silane may have up to four chemical moieties bonded toit, and in some cases, one of the moieties may be on RO-moiety, where Ris an alkoxide or other chemical moieity, for example, so that thesilane can become incorporated into a metal oxide-based network. Inaddition, in some cases, one or more of the silanes may be hydrolyzed toform the corresponding silanol.

In addition, it should be understood that the sol-gel is not limited tocontaining only silanes, and other materials may be present in additionto, or in place of, the silanes. For instance, the coating may includeone or more metal oxides, such as SiO₂, vanadia (V₂O₅), titania (TiO₂),and/or alumina (Al₂O₃). As other examples, the sol-gel may comprisemoieties containing double bonds, or otherwise are reactive within anypolymerization reactions, for example, thiols for participation inradical polymerization.

The substrate may be any suitable material able to receive the sol-gel,for example, glass, metal oxides, or polymers such aspolydimethylsiloxane (PDMS) and other siloxane polymers. In some cases,the substrate may be one in which contains silicon atoms, and in certaininstances, the substrate may be chosen such that it contains silanol(Si—OH) groups, or can be modified to have silanol groups. For instance,the substrate may be exposed to an oxygen plasma, an oxidant, or astrong acid or a strong base cause the formation of silanol groups onthe substrate. The substrate may have any suitable shape, for example, aflat surface, a microfluidic channel, etc.

The sol-gel may be present as a coating on the substrate, and thecoating may have any suitable thickness. For instance, the coating mayhave a thickness of no more than about 100 micrometers, no more thanabout 30 micrometers, no more than about 10 micrometers, no more thanabout 3 micrometers, or no more than about 1 micrometer. Thickercoatings may be desirable in some cases, for instance, in applicationsin which higher chemical resistance is desired. However, thinnercoatings may be desirable in other applications, for instance, withinrelatively small microfluidic channels.

In one set of embodiments, the hydrophobicity of the sol-gel coating canbe controlled, for instance, such that a first portion of the sol-gelcoating is relatively hydrophobic, and a second portion of the sol-gelcoating is more or less relatively hydrophobic than the first portion.The hydrophobicity of the coating can be determined using techniquesknown to those of ordinary skill in the art, for example, using contactangle measurements such as those discussed below. For instance, in somecases, a first portion of a substrate (e.g., within a microfluidicchannel) may have a hydrophobicity that favors an organic solvent towater, while a second portion may have a hydrophobicity that favorswater to the organic solvent.

The hydrophobicity of the sol-gel coating can be modified, for instance,by exposing at least a portion of the sol-gel coating to a condensationor polymerization reaction to react a polymer to the sol-gel coating.The polymer reacted to the sol-gel coating may be any suitable polymer,and may be chosen to have certain hydrophobicity properties. Forinstance, the polymer may be chosen to be more hydrophobic or morehydrophilic than the substrate and/or the sol-gel coating. As anexample, a hydrophilic polymer that could be used is poly(acrylic acid).

The polymer may be added to the sol-gel coating by supplying the polymerin monomeric (or oligomeric) form to the sol-gel coating (e.g., insolution), and causing a condensation or polymerization reaction tooccur between the polymer and the sol-gel. For instance, free radicalpolymerization may be used to cause bonding of the polymer to thesol-gel coating. In some embodiments, a reaction such as free radicalpolymerization may be initiated by exposing the reactants to heat and/orlight, such as ultraviolet (UV) light, optionally in the presence of aphotoinitiator able to produce free radicals (e.g., via molecularcleavage) upon exposure to light. Those of ordinary skill in the artwill be aware of many such photoinitiators, many of which arecommercially available, such as Irgacur 2959 (Ciba Specialty Chemicals),aminobenzophenone, benzophenone, or2-hydroxy-4-(3-triethoxysilylpropoxy)-diphenylketone (SIH6200.0, ABCRGmbH & Co. KG).

The photoinitiator may be included with the polymer added to the sol-gelcoating, or in some cases, the photoinitiator may be present within thesol-gel coating. The photoinitiators may also be introduced within thesol-gel coating after the coating step, in some cases. As an example, aphotoinitiator may be contained within the sol-gel coating, andactivated upon exposure to light. The photoinitiator may also beconjugated or bonded to a component of the sol-gel coating, for example,to a silane. As an example, a photoinitiator such as Irgacur 2959 may beconjugated to a silane-isocyanate via a urethane bond (where a primaryalcohol on the photoinitiator may participate in nucleophilic additionwith the isocyanate group, which may produce a urethane bond).

It should be noted that only a portion of the sol-gel coating may bereacted with a polymer, in some embodiments of the invention. Forinstance, the monomer and/or the photoinitiator may be exposed to only aportion of the substrate, or the condensation or polymerization reactionmay be initiated in only a portion of the substrate. As a particularexample, a portion of the substrate may be exposed to light, while otherportions are prevented from being exposed to light, for instance, by theuse of masks or filters. Accordingly, different portions of thesubstrate may exhibit different hydrophobicities, as condensation orpolymerization does not occur everywhere on the substrate. As anotherexample, the substrate may be exposed to UV light by projecting ade-magnified image of an exposure pattern onto the substrate. In somecases, small resolutions (e.g., 1 micrometer, or less) may be achievedby projection techniques.

Another aspect of the present invention is generally directed at systemsand methods for coating such a sol-gel onto at least a portion of asubstrate. It should be understood in the descriptions below, however,that for a sol-gel that is coated “on” at least a portion of thesubstrate, at least some of the sol-gel may become embedded within thesubstrate, e.g., as certain silanes may be able to diffuse into PDMS. Infact, such diffusion may facilitate the coating and positioning of thesol-gel onto the substrate.

In one set of embodiments, a substrate, such as a microfluidic channel,is exposed to a sol, which is then treated to form a sol-gel coating. Insome cases, the sol can also be pretreated to cause partial condensationor polymerization to occur. Extra sol-gel coating may optionally beremoved from the substrate. In some cases, as discussed, a portion ofthe coating may be treated to alter its hydrophobicity (or otherproperties), for instance, by exposing the coating to a solutioncontaining a monomer and/or an oligomer, and causing condensation orpolymerization of the monomer and/or oligomer to occur with the coating.

The sol may be contained within a solvent, which can also contain othercompounds such as photoinitiators including those described above. Insome cases, the sol may also comprise one or more silane compounds. Thesol may be treated to form a gel using any suitable technique, forexample, by removing the solvent using chemical or physical techniques,such as heat. For instance, the sol may be exposed to a temperature ofat least about 50° C., at least about 100° C., at least about 150° C.,at least about 200° C., or at least about 250° C., which may be used todrive off or vaporize at least some of the solvent. As a specificexample, the sol may be exposed to a hotplate set to reach a temperatureof at least about 200° C. or at least about 250° C., and exposure of thesol to the hotplate may cause at least some of the solvent to be drivenoff or vaporized. In some cases, however, the sol-gel reaction mayproceed even in the absence of heat, e.g., at room temperature. Thus,for instance, the sol may be left alone for a while (e.g., about anhour, about a day, etc.), and/or air or other gases, or liquids, may bepassed over the sol, to allow the sol-gel reaction to proceed.

In other embodiments, other techniques of initiation may be used insteadof or in addition to photoinitiators. Examples inculde, but are notlimited to, redox initiation, thermal decomposition triggered by e.g.heating portions of a device (e.g., this can be done by liquid streamsthat have a certain temperature or contain an oxidizing or a reducingchemical). In another embodiment, functionalization of the surfaces maybe achieved by polyaddition and polycondensation reactions, forinstance, if the surface contains reactive groups that can participatein the reaction. Silanes containing a desired functionality may also beadded in some cases, e.g., silanes containing COOH moieties, NH₂moieties, SO₃H moieties, SO₄H moieties, OH moieties, PEG-chains, or thelike).

In some cases, any ungelled sol that is still present may be removedfrom the substrate. The ungelled sol may be actively removed, e.g.,physically, by the application of pressure or the addition of a compoundto the substrate, etc., or the ungelled sol may be removed passively insome cases. For instance, in some embodiments, a sol present within amicrofluidic channel may be heated to vaporize solvent, which builds upin a gaseous state within the microfluidic channels, thereby increasingpressure within the microfluidic channels. The pressure, in some cases,may be enough to cause at least some of the ungelled sol to be removedor “blown” out of the microfluidic channels.

In certain embodiments, the sol is pretreated to cause partialcondensation to occur, prior to exposure to the substrate. For instance,the sol may be treated such that partial condensation occurs within thesol. The sol may be treated, for example, by exposing the sol to an acidor a base, or to temperatures that are sufficient to cause at least somegellation to occur. In some cases, the temperature may be less than thetemperature the sol will be exposed to when added to the substrate. Somecondensation of the sol may occur, but the condensation may be stoppedbefore reaching completion, for instance, by reducing the temperature.Thus, within the sol, some oligomers or other complex structures (e.g.,branched structures or spherical structures) may form (which may notnecessarily be well-characterized in terms of length), although fullcondensation has not yet occurred. The partially treated sol may then beadded to the substrate, as discussed above.

In certain embodiments, a portion of the coating may be treated to alterits hydrophobicity (or other properties) after the coating has beenintroduced to the substrate. In some cases, the coating is exposed to asolution containing a monomer and/or an oligomer, which is thencondensed or polymerized to bond to the coating, as discussed above. Forinstance, a portion of the coating may be exposed to heat or to lightsuch as ultraviolet right, which may be used to initiate a free radicalpolymerization reaction to cause polymerization to occur. Optionally, aphotoinitiator may be present, e.g., within the sol-gel coating, tofacilitate this reaction. In some embodiments, the photoinitiator mayalso contain double bonds, thiols, and/or other reactive groups suchthat the monomers and/or oligomers can be covalently linked to thesol-gel coating.

As discussed, in some aspects of the invention, a microfluidic channelmay be coated in a sol-gel material. “Microfluidic,” as used herein,refers to a device, apparatus or system including at least one fluidchannel having a cross-sectional dimension of less than about 1millimeter (mm), and in some cases, a ratio of length to largestcross-sectional dimension of at least 3:1. One or more conduits of thesystem may be a capillary tube. In some cases, multiple conduits areprovided, and in some embodiments, at least some are nested, asdescribed herein. The conduits may be in the microfluidic size range andmay have, for example, average inner diameters, or portions having aninner diameter, of less than about 1 millimeter, less than about 300micrometers, less than about 100 micrometers, less than about 30micrometers, less than about 10 micrometers, less than about 3micrometers, or less than about 1 micrometer, thereby providing dropletshaving comparable average diameters. One or more of the conduits may(but not necessarily), in cross section, have a height that issubstantially the same as a width at the same point. Conduits mayinclude an orifice that may be smaller, larger, or the same size as theaverage diameter of the conduit. For example, conduit orifices may havediameters of less than about 1 mm, less than about 500 micrometers, lessthan about 300 micrometers, less than about 200 micrometers, less thanabout 100 micrometers, less than about 50 micrometers, less than about30 micrometers, less than about 20 micrometers, less than about 10micrometers, less than about 3 micrometers, etc. In cross-section, theconduits may be rectangular or substantially non-rectangular, such ascircular or elliptical.

A “channel,” as used herein, means a feature on or in an article(substrate) that at least partially directs flow of a fluid. The channelcan have any cross-sectional shape (circular, oval, triangular,irregular, square or rectangular, or the like) and can be covered oruncovered. In embodiments where it is completely covered, at least oneportion of the channel can have a cross-section that is completelyenclosed, or the entire channel may be completely enclosed along itsentire length with the exception of its inlet(s) and/or outlet(s). Achannel may also have an aspect ratio (length to average cross sectionaldimension) of at least 2:1, more typically at least 3:1, 5:1, 10:1,15:1, 20:1, or more. An open channel generally will includecharacteristics that facilitate control over fluid transport, e.g.,structural characteristics (an elongated indentation) and/or physical orchemical characteristics (hydrophobicity vs. hydrophilicity) or othercharacteristics that can exert a force (e.g., a containing force) on afluid. The fluid within the channel may partially or completely fill thechannel. In some cases where an open channel is used, the fluid may beheld within the channel, for example, using surface tension (i.e., aconcave or convex meniscus).

The channel may be of any size, for example, having a largest dimensionperpendicular to fluid flow of less than about 5 mm or 2 mm, or lessthan about 1 mm, or less than about 500 microns, less than about 200microns, less than about 100 microns, less than about 60 microns, lessthan about 50 microns, less than about 40 microns, less than about 30microns, less than about 25 microns, less than about 10 microns, lessthan about 3 microns, less than about 1 micron, less than about 300 nm,less than about 100 nm, less than about 30 nm, or less than about 10 nm.In some cases the dimensions of the channel may be chosen such thatfluid is able to freely flow through the article or substrate. Thedimensions of the channel may also be chosen, for example, to allow acertain volumetric or linear flowrate of fluid in the channel. Ofcourse, the number of channels and the shape of the channels can bevaried by any method known to those of ordinary skill in the art. Insome cases, more than one channel or capillary may be used. For example,two or more channels may be used, where they are positioned inside eachother, positioned adjacent to each other, positioned to intersect witheach other, etc.

In some cases, relatively large numbers of devices may be used inparallel, for example at least about 10 devices, at least about 30devices, at least about 50 devices, at least about 75 devices, at leastabout 100 devices, at least about 200 devices, at least about 300devices, at least about 500 devices, at least about 750 devices, or atleast about 1,000 devices or more may be operated in parallel. Thedevices may comprise different conduits (e.g., concentric conduits),orifices, microfluidics, etc. In some cases, an array of such devicesmay be formed by stacking the devices horizontally and/or vertically.The devices may be commonly controlled, or separately controlled, andcan be provided with common or separate sources of various fluids,depending on the application.

In some cases, such coating techniques may be useful in the creation ofmultiple emulsions, such as those described in International PatentApplication No. PCT/US2006/007772, filed Mar. 3, 2006, entitled “Methodand Apparatus for Forming Multiple Emulsions,” by Weitz, et al.,published as WO 2006/096571 on Sep. 14, 2006; U.S. Provisional PatentApplication Ser. No. 60/920,574, filed Mar. 28, 2007, entitled “MultipleEmulsions and Techniques for Formation,” by Chu, et al., in U.S. patentapplication Ser. No. 12/058,628, filed on Mar. 28, 2008, entitled“Emulsions and Techniques for Formation,” by Chu, et al., or in aInternational Patent Application Serial No. PCT/US2008/004097, filed onMar. 28, 2008, entitled “Emulsions and Techniques for Formation,” byChu, et al., each incorporated herein by reference. For instance, in oneset of embodiments, to create a multiple emulsion, an inner droplet maycreated using a first droplet maker and an outer droplet may be createdusing a second droplet maker. Optionally, this may be extended to athird droplet maker, a fourth droplet maker, etc. The droplet makers maybe constructed such that they exhibit different hydrophobicities. In oneembodiment, coating techniques such as those described herein are usedto control the hydrophobicities. For example, a first droplet maker maybe coated such that it is more hydrophobic than a second droplet maker(or vice versa). A non-limiting example of such a system is described inthe Examples, below.

A variety of materials and methods, according to certain aspects of theinvention, can be used to form systems such as those described above. Insome cases, the various materials selected lend themselves to variousmethods. For example, various components of the invention can be formedfrom solid materials, in which the channels can be formed viamicromachining, film deposition processes such as spin coating andchemical vapor deposition, laser fabrication, photolithographictechniques, etching methods including wet chemical or plasma processes,and the like. See, for example, Scientific American, 248:44-55, 1983(Angell, et al.). In one embodiment, at least a portion of the fluidicsystem is formed of silicon by etching features in a silicon chip.Technologies for precise and efficient fabrication of various fluidicsystems and devices of the invention from silicon are known. In anotherembodiment, various components of the systems and devices of theinvention can be formed of a polymer, for example, an elastomericpolymer such as polydimethylsiloxane (“PDMS”), polytetrafluoroethylene(“PTFE” or Teflon®), or the like.

Different components can be fabricated of different materials. Forexample, a base portion including a bottom wall and side walls can befabricated from an opaque material such as silicon or PDMS, and a topportion can be fabricated from a transparent or at least partiallytransparent material, such as glass or a transparent polymer, forobservation and/or control of the fluidic process. In other embodiments,however, the components need not be transparent or partiallytransparent, depending on the application. Components can be coated soas to expose a desired chemical functionality to fluids that contactinterior channel walls, where the base supporting material does not havea precise, desired functionality. For example, components can befabricated as illustrated, with interior channel walls coated withanother material. Material used to fabricate various components of thesystems and devices of the invention, e.g., materials used to coatinterior walls of fluid channels, may desirably be selected from amongthose materials that will not adversely affect or be affected by fluidflowing through the fluidic system, e.g., material(s) that is chemicallyinert in the presence of fluids to be used within the device.

In one embodiment, various components of the invention are fabricatedfrom polymeric and/or flexible and/or elastomeric materials, and can beconveniently formed of a hardenable fluid, facilitating fabrication viamolding (e.g. replica molding, injection molding, cast molding, etc.).The hardenable fluid can be essentially any fluid that can be induced tosolidify, or that spontaneously solidifies, into a solid capable ofcontaining and/or transporting fluids contemplated for use in and withthe fluidic network. In one embodiment, the hardenable fluid comprises apolymeric liquid or a liquid polymeric precursor (i.e. a “prepolymer”).Suitable polymeric liquids can include, for example, thermoplasticpolymers, thermoset polymers, or mixture of such polymers heated abovetheir melting point. As another example, a suitable polymeric liquid mayinclude a solution of one or more polymers in a suitable solvent, whichsolution forms a solid polymeric material upon removal of the solvent,for example, by evaporation. Such polymeric materials, which can besolidified from, for example, a melt state or by solvent evaporation,are well known to those of ordinary skill in the art. A variety ofpolymeric materials, many of which are elastomeric, are suitable, andare also suitable for forming molds or mold masters, for embodimentswhere one or both of the mold masters is composed of an elastomericmaterial. A non-limiting list of examples of such polymers includespolymers of the general classes of silicone polymers, epoxy polymers,and acrylate polymers. Epoxy polymers are characterized by the presenceof a three-membered cyclic ether group commonly referred to as an epoxygroup, 1,2-epoxide, or oxirane. For example, diglycidyl ethers ofbisphenol A can be used, in addition to compounds based on aromaticamine, triazine, and cycloaliphatic backbones. Another example includesthe well-known Novolac polymers. Non-limiting examples of siliconeelastomers suitable for use according to the invention include thoseformed from precursors including the chlorosilanes such asmethylchlorosilanes, ethylchlorosilanes, phenylchlorosilanes, etc.

Silicone polymers are preferred in one set of embodiments, for example,the silicone elastomer polydimethylsiloxane. Non-limiting examples ofPDMS polymers include those sold under the trademark Sylgard by DowChemical Co., Midland, Mich., and particularly Sylgard 182, Sylgard 184,and Sylgard 186. Silicone polymers including PDMS have severalbeneficial properties simplifying fabrication of the microfluidicstructures of the invention. For instance, such materials areinexpensive, readily available, and can be solidified from aprepolymeric liquid via curing with heat. For example, PDMSs aretypically curable by exposure of the prepolymeric liquid to temperaturesof about, for example, about 65° C. to about 75° C. for exposure timesof, for example, about an hour. Also, silicone polymers, such as PDMS,can be elastomeric, and thus may be useful for forming very smallfeatures with relatively high aspect ratios, necessary in certainembodiments of the invention. Flexible (e.g., elastomeric) molds ormasters can be advantageous in this regard. Another example of suitablepolymers are polyhydroxyalkanoates such aspoly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

One advantage of forming structures such as microfluidic structures ofthe invention from silicone polymers, such as PDMS, is the ability ofsuch polymers to be oxidized, for example by exposure to anoxygen-containing plasma such as an air plasma, so that the oxidizedstructures contain, at their surface, chemical groups capable ofcross-linking to other oxidized silicone polymer surfaces or to theoxidized surfaces of a variety of other polymeric and non-polymericmaterials. Thus, components can be fabricated and then oxidized andessentially irreversibly sealed to other silicone polymer surfaces, orto the surfaces of other substrates reactive with the oxidized siliconepolymer surfaces, without the need for separate adhesives or othersealing means. In most cases, sealing can be completed simply bycontacting an oxidized silicone surface to another surface without theneed to apply auxiliary pressure to form the seal. That is, thepre-oxidized silicone surface acts as a contact adhesive againstsuitable mating surfaces. Specifically, in addition to beingirreversibly sealable to itself, oxidized silicone such as oxidized PDMScan also be sealed irreversibly to a range of oxidized materials otherthan itself including, for example, glass, silicon, silicon oxide,quartz, silicon nitride, polyethylene, polystyrene, glassy carbon, andepoxy polymers, which have been oxidized in a similar fashion to thePDMS surface (for example, via exposure to an oxygen-containing plasma).Oxidation and sealing methods useful in the context of the presentinvention, as well as overall molding techniques, are described in theart, for example, in an article entitled “Rapid Prototyping ofMicrofluidic Systems and Polydimethylsiloxane,” Anal. Chem., 70:474-480,1998 (Duffy, et al.), incorporated herein by reference.

In some embodiments, certain microfluidic structures of the invention(or interior, fluid-contacting surfaces) may be formed from certainoxidized silicone polymers. Such surfaces may be more hydrophilic thanthe surface of an elastomeric polymer. Such hydrophilic channel surfacescan thus be more easily filled and wetted with aqueous solutions. Suchsurfaces may be useful for sol-gel coatings.

In one embodiment, a bottom wall of a microfluidic device of theinvention is formed of a material different from one or more side wallsor a top wall, or other components. For example, the interior surface ofa bottom wall can comprise the surface of a silicon wafer or microchip,or other substrate. Other components can, as described above, be sealedto such alternative substrates. Where it is desired to seal a componentcomprising a silicone polymer (e.g. PDMS) to a substrate (bottom wall)of different material, the substrate may be selected from the group ofmaterials to which oxidized silicone polymer is able to irreversiblyseal (e.g., glass, silicon, silicon oxide, quartz, silicon nitride,polyethylene, polystyrene, epoxy polymers, and glassy carbon surfaceswhich have been oxidized). Alternatively, other sealing techniques canbe used, as would be apparent to those of ordinary skill in the art,including, but not limited to, the use of separate adhesives, bonding,solvent bonding, ultrasonic welding, etc.

The following applications are each incorporated herein by reference:U.S. patent application Ser. No. 08/131,841, filed Oct. 4, 1993,entitled “Formation of Microstamped Patterns on Surfaces and DerivativeArticles,” by Kumar, et al., now U.S. Pat. No. 5,512,131, issued Apr.30, 1996; U.S. patent application Ser. No. 09/004,583, filed Jan. 8,1998, entitled “Method of Forming Articles including Waveguides viaCapillary Micromolding and Microtransfer Molding,” by Kim, et al., nowU.S. Pat. No. 6,355,198, issued Mar. 12, 2002; International PatentApplication No. PCT/US96/03073, filed Mar. 1, 1996, entitled“Microcontact Printing on Surfaces and Derivative Articles,” byWhitesides, et al., published as WO 96/29629 on Jun. 26, 1996;International Patent Application No.: PCT/US01/16973, filed May 25,2001, entitled “Microfluidic Systems including Three-DimensionallyArrayed Channel Networks,” by Anderson, et al., published as WO 01/89787on Nov. 29, 2001; U.S. patent application Ser. No. 11/246,911, filedOct. 7, 2005, entitled “Formation and Control of Fluidic Species,” byLink, et al., published as U.S. Patent Application Publication No.2006/0163385 on Jul. 27, 2006; U.S. patent application Ser. No.11/024,228, filed Dec. 28, 2004, entitled “Method and Apparatus forFluid Dispersion,” by Stone, et al., published as U.S. PatentApplication Publication No. 2005/0172476 on Aug. 11, 2005; InternationalPatent Application No. PCT/US2006/007772, filed Mar. 3, 2006, entitled“Method and Apparatus for Forming Multiple Emulsions,” by Weitz, et al.,published as WO 2006/096571 on Sep. 14, 2006; U.S. patent applicationSer. No. 11/360,845, filed Feb. 23, 2006, entitled “Electronic Controlof Fluidic Species,” by Link, et al., published as U.S. PatentApplication Publication No. 2007/000342 on Jan. 4, 2007; and U.S. patentapplication Ser. No. 11/368,263, filed Mar. 3, 2006, entitled “Systemsand Methods of Forming Particles,” by Garstecki, et al. Alsoincorporated herein by reference are U.S. Provisional Patent ApplicationSer. No. 60/920,574, filed Mar. 28, 2007, entitled “Multiple Emulsionsand Techniques for Formation,” by Chu, et al., U.S. Patent ApplicationSer. No. 60/920,574, filed on Mar. 28, 2007, entitled “Emulsions andTechniques for Formation,” by Chu, et al., International PatentApplication Serial No. PCT/US2008/004097, filed on Mar. 28, 2007,entitled “Emulsions and Techniques for Formation,” by Chu, et al., andU.S. Provisional Patent Application Ser. No. 61/040,442, filed Mar. 28,2008, entitled “Surfaces, Including Microfluidic Channels, WithControlled Wetting Properties,” by Abate, et al.

The following examples are intended to illustrate certain embodiments ofthe present invention, but do not exemplify the full scope of theinvention.

EXAMPLE 1

This example illustrates a system that combines the simplicity ofstamped polydimethylsiloxane (PDMS) devices with the chemical robustnessand precision control of the interface of glass. This example usessol-gel chemistry to coat PDMS channels with a photoactive, chemicallyresistant sol-gel layer. In addition, this example shows that with theincorporation of functional compounds into the coating, the propertiesof the coated interface can be precisely engineered. By incorporatingfluorosilanes into the coating, a hydrophobic interface can be produced,suitable for the formation of inverted water-in-oil emulsions. Byincorporating a photoactive silane into the coating, the coatedinterface can be spatially modified through UV graft-polymerization.This allows simple production of microfluidic devices having sharpcontrasts in wetting, which can be use to produce multiple emulsions,such as those described in a U.S. patent application filed on even dateherewith, entitled “Emulsions and Techniques for Formation,” by Chu, etal.

The photoactive sol-gel coating in this example contains a photoiniatorcoupled to a silane that is embedded in the sol-gel network. To makethis molecule, combined are 11.0 g Irgacur 2959, 0.01 g hydroquinone,and 49.4 microliters dibutyltin dilaurate in 20.0 mL of dry chloroform.This was stirred under nitrogen until the mixture is homogeneous, andslowly added was 12.1 mL silane-isocyanate over 30 min. The mixture wasthen stirred for 3 hours at 50° C. to allow the reaction to complete.During this time, the primary alcohol of the Irgacur is belived toparticipates in nucleophilic addition with the isocyanate group, forminga urethane bond. The reaction was performed in a dry environment toreduce the possibility side reactions. This yielded a pure product,which was verified by thin layer chromatography (TLC). To concentratethe reaction product, the chloroform is removed under vacuum, yielding ayellowish solid which was used without further purification. To preparethe photoactive sol precursor mixture, combined were 1 mL TEOS(tetraethyl orthosilicate), 1 mL MTES (methyltriethoxy silane), 0.5 mLheptadecafluorosilane, 0.5 g Irgacur-silane, 1 mL trifluoroethanol, and1 mL pH 2 H₂O adjusted with hydrochloric acid. The solution was heatedon a 200° C. hotplate for 5 min until it turned clear. The acidcatalyzed condensation and the hydrolysis reactions of the alkoxysilanes. The hydrolysis reactions also cleaved ethoxy groups from thesilanes, converting them into hydroxyl groups. The silane monomers werecouple with one another through hydrolysis and condensation to yieldhigher molecular weight compounds. The resulting oligmer precursors weremiscible with PDMS, preventing swelling. In addition, the preconversionalso reduced contraction and cracking during gelation, yielding morehomogeneous coatings.

The PDMS channels were treated with oxygen plasma to generate silanolgroups just before they were sealed by bonding to a glass slide. Thebonded device was then immediately flushed with the preconvertedphotoactive sol mixture. The preconverted siloxanes reacted with thehydroxyl groups on the PDMS and the glass to form covalent silica bonds.To initiate the gelation reaction, the devices were placed on a 250° C.hotplate with the bottom glass slide in contact with the hotplate. Thehigh temperature initiated gelation while vaporizing the solvent. Thiscaused pressure to build in the channels, which blew them clear and leftbehind the desired coating.

The thickness of the coating increased with the viscosity of thesol-mixture and decreased with the temperature of the hotplate. Forinstance, thicker coatings may be appropriate for larger channels inwhich higher chemical resistance is desired. To deposit a thickercoating, more highly preconverted viscous sol mixtures and lowerhotplate temperatures (e.g., around 150° C.) may be used. Thinnercoatings could also be applied to channels with features smaller than 10micrometers without clogging. To deposit thinner coatings, the viscosityof the sol mixture could be lowered, for instance, by diluting with anequal part or greater of methanol, which has a lower vaporizationtemperature, and the hotplate temperature could be increased (e.g., to250° C.).

The photoiniatior in the coating allowed spatial functionanlization ofthe channels through UV graft polymerization. A monomer solution wasprepared by combining 0.2 mL of acrylic acid with 0.8 mL 5 M NaIO₄ H₂O,1 mL ethanol, 0.5 mL acetone and 0.05 g benzophenone. The NaIO₄ andbenzopehone were added in this case to speed polymerization. The devicewas then filled with the monomer solution and irradiated with UV lightwherever polymerization was desired. The UV light generated radicals bycleaving the photoinitiator molecules, initiating polymerization. Thegrowing acrylic acid polymers were tethered to the sol-gel networkthrough covalent linkages with the initiator-silanes and throughcross-linkages with one another through the benzophenone; thebenzophenone also abstracts hydrogen from methyl groups in the coating,which may increase interfacial bonding. The thickness of the polymerizedlayer depended on the intensity and duration of the UV exposure,affording additional control over the wetting change of the interface.

To achieve micrometer scale UV pattern resolution, a de-magnified imageof the field diaphragm of a Koehler Illumination path was projected ontothe sample. UV-transparent fused silica lenses were used to ensure UVtransmission to the sample. A liquid-fiber mercury arc-lamp was used forillumantion. The size of the illuminated field, and therefore, the sizeof the polymerized region, can be controlled by dialing the fielddiaphragm. The intensity of the illuminated field, and therfore, therate at which polymerization progresses, could be adjusted by dialingthe condenser diaphragm. Moreover, various patterned photomasks could beplaced at the field diagram to project a more sophisticated pattern. Thechannels here were irradiated for 1-5 min, depending on their dimensionsand the desired thickness of the polymer layer, and these conditions maybe optimized using no more than routine skill, depending on theparticular application. For instance, smaller channels coated with athin sol-gel layer required longer irradiation times than large channelscoated with a thick sol-gel layer.

To directly observe the coating, scanning electron micrograph (SEM)images of channel cross-sections were captured. FIG. 1 illustrates SEMimages of channel cross sections prepared as discussed above. The PDMSchannels were coated with a thin layer of sol-gel using a low viscositysol mixture and a 250° C. hotplate temperature. The uncoated PDMSchannels were initially rectangular in shape, exhibiting clean PDMSwalls, as shown in FIGS. 1A-1B. However, the delicate wavy pattern ofthe initial PDMS side walls, which is an artifact of thesoft-lithography process, were smoothed over by the sol-gel coating, asshown by the coated channel cross-section in FIG. 1C. The corners of thecoated channels were also rounded-off because the coating liquid wettedchannels and collected in the corners, as shown in FIG. 1D. A region ofthe coated device was functionalized with acrylic acid using UV graftpolymerization. The grafted polymer was deposited as a thin layer on thesurface of the sol-gel, as shown in FIG. 1E. The grafted polymer wascovalently linked to the sol-gel through bonds with the photoactivesilane. As the polymer layer grew, a pattern developed on the channelwalls, as shown in FIG. 1F. The images in FIGS. 1B, 1D, and 1F showhigher magnification images upper-right corner of each of thecross-sections of FIGS. 1A, 1C, and 1E, respectively. All scale barsdenote 5 micrometers.

To verify that the grafted polymer was permanently deposited onto thesol-gel interface, fourier transform infrared spectroscopy (FTIR)measurements were performed on coated and polyacrylic acid graftedsubstrates. FTIR allows the identification of the proportion of chemicalgroups in the coating before and after polymerization. Before grafting,the FTIR spectrum of the coating showed a peak at the wavenumber 1670and 1700, as shown in FIG. 2A. These peaks corresponded to the carbonylgroups of the urethane linkage in the photoactive silane. Afterpolymerization, the peak at 1700 increased in amplitude and broadeneddue to the addition of a large number of carbonyl groups in thepolyacrylic acid grafted to the surface, as shown in FIG. 2A.

To determine the functional wetting properties of the coating before andafter grafting, contact angle measurements were performed with waterdroplets. A glass slide was coated with the photoactive sol-gel and halfof of the slide was functionalized with polyacrylic acid. A waterdroplet was placed on each half of the slide and images were captured tomeasure the contact angle. The native coating was hydrophobic due to theaddition of fluorosilane to the coating mixture; thus, the water dropletbeaded-up, forming a contact angle of about 106°, as shown in FIG. 2A.Such a contact angle is consistent with that of a fluorinated surface,and may be used for the production of inverted water-in-fluorocarbon oilemulsions in a coated microfluidic device. By contrast, the waterdroplet spread out in the polyacrylic acid grafted half of the slide,forming a contact angle of about 5°, as shown in FIG. 2B. Such ahydrophilic device may be used for the production of direct oil-in-wateremulsions in a coated, PAA grafted microfluidic device.

To characterize the surface topography of the coating, atomic forcemicroscopy (AFM) images were captured of both coated and coated/graftedmicrochannels. The native coating was smooth and showed little structurein the AFM images, as shown in FIG. 3A. By contrast, the portion of thechannel on which polyacrylic acid had been grafted showed a richtopographical structure, as shown in FIG. 3B. The images show a 5×10micrometer area; dark to light colour scale maps to 0 to 150 nm highfeature sizes. In fact, when polymerization is viewed with a brightfieldmicroscope, ridged reptilations can be seen to gradually develop in thegrafted region. The amplitude of the reptilations increased with theamount of polymer that was grafted to the interface.

To quantify the resolution with which the polymer can be grafted, aspatially modified channel was stained with toluidene blue, a dye thatelectrostatically binds to polyacrylic acid. The channels were filledwith 0.1% by weight aqueous dye solution and allowed to sit for 1 min.The solution was then flushed out with 1 mL of H₂O. A brightfield imageof the spatially grafted and stained channel is shown in FIG. 3C; thePDMS channel has been coated and, on the right, PAA grafted. Thepolyacrylic acid has been stained with Toluidene Blue. To quantifyspatial precision of the grafting, the average intensity across thechannel was computed and plotted as a function of channel length, asshown in in FIG. 3D. From the intensity profile the reptilations areseen to have a characteristic wavelength of about 2-3 micrometers forthis particular device. The contrast between the coated and graftedregions was also estimated to be about 5 micrometers, as shown by theregion demarcated in gray in FIG. 3D.

EXAMPLE 2

The coating discussed in Example 1 can allow PDMS channels to bemodified so as to have sharp contrasts in wetting. This may be usefulfor a number of applications, including inversion of an emulsion and theformation of multiple emulsions, and/or to prevent adsorption or foulingfrom occurring. As a demonstration, in this example, multiple emulsionswere produced in coated, spatially grafted PDMS devices. For theemulsions, water and fluorocarbon oil (Fluorinert FC40) stabilized bysurfactants Zonyl FSN-100 (Sigma-Aldrich) and Krytox 157FSL (Dupont)were used. For a double emulsion, a device having two flow-focusdrop-makers arranged in series, as shown in FIG. 4A, was coated. Thebare coating was hydrophobic due to the high concentration offluorosilane in the sol-gel network; thus, after coating, the firstdrop-maker produced an inverted water-in-oil emulsion, as shown in FIG.4A. By contrast, after graft-polymerization of polyacrylic acid thesecond drop-maker is made hydrophilic; this allowed emulsification ofthe oil continuous phase of the first drop-maker for the production ofwater-in-oil-in-water double emulsions, as shown in FIG. 4A. The scalebars in FIG. 4 is 60 micrometers.

To produce triple emulsions, a third stage of droplet making wasconcatenated onto the device, and the second dropmaker wasfunctionalized to make it hydrophilic; the native wetting properties ofthe coating made the other dropmaker stages hydrophobic. Using onlyFC40, H₂O and surfactant for all phases, W/O/W/O triple emulsions ofvarious morphologies were produced, as shown in FIGS. 4B-4D. Themorphology of the mutliple emulsion depended on the flow rates of theinjected phases and the geometry of the dropmaker stages. In particular,in this particular example, the greatest control over droplet morphologywas obtained when the height of the device is fixed equal to the widthof the smallest dropmaker, and the width of the subsequent dropmakerswere gradually scaled-up.

The chemistry of the sol-gel mixture can be engineered to control theinherent wetting properties of the coating; this allows production ofemulsions without further functionalization. The wetting properties ofthe coated channels could be spatially modified through UV graftpolymerization; this produced chemically resistant channels with sharpcontrasts in wetting, which can be used to produce multiple emulsions,or in other suitable applications.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, kit, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,kits, and/or methods, if such features, systems, articles, materials,kits, and/or methods are not mutually inconsistent, is included withinthe scope of the present invention.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to thecontrary, in any methods claimed herein that include more than one stepor act, the order of the steps or acts of the method is not necessarilylimited to the order in which the steps or acts of the method arerecited.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

What is claimed is:
 1. An article, comprising: a sol-gel coating coatedon at least a portion of a microfluidic channel, wherein the sol-gelcomprises a moiety containing a double bond.
 2. The article of claim 1,wherein the microfluidic channel is defined within a microfluidic devicecomprising polydimethylsiloxane.
 3. The article of claim 1, wherein themicrofluidic channel is defined within a microfluidic device comprisingglass.
 4. The article of claim 1, wherein a first portion of the sol-gelcoating is relatively hydrophobic, and a second portion of the sol-gelcoating is relatively hydrophilic.
 5. The article of claim 1, whereinthe coating comprises a silane.
 6. The article of claim 1, wherein thecoating comprises a fluorosilane.
 7. The article of claim 1, wherein thecoating comprises heptadecafluorooctylsilane.
 8. The article of claim 1,wherein the coating comprises heptadecafluorosilane.
 9. The article ofclaim 1, wherein the coating comprises a photoinitiator.
 10. (canceled)11. The article of claim 1, wherein the coating comprises a moietycomprising a thiol.
 12. The article of claim 9, wherein thephotoinitiator is chemically coupled to a silane.
 13. The article ofclaim 12, wherein the photoinitiator is coupled to the silane via aurethane bond.
 14. The article of claim 9, wherein the photoinitiator isIrgacure
 2959. 15. The article of claim 1, wherein the sol-gel coatinghas a thickness of no more than about 10 micrometers.
 16. The article ofclaim 1, wherein at least a portion of the sol-gel coating containsacrylic acid.
 17. The article of claim 1, wherein at least a portion ofthe sol-gel coating comprises acrylic acid.
 18. The article of claim 17,wherein the acrylic acid is chemically bonded to the sol-gel coating.19. The article of claim 1, wherein the portion of the sol-gel coatingcomprising acrylic acid is less hydrophobic than a portion of thesol-gel coating free of acrylic acid. 20-60. (canceled)